DMux8Way(ERROR MESSAGE:"can't connect gate's output pin to part")

DMux8Way(ERROR MESSAGE:"can't connect gate's output pin to part")

CHIP DMux8Way {
IN in, sel[3];
OUT a, b, c, d, e, f, g, h;

PARTS:
DMux4Way(in=in,sel=sel[1..2],a=q,b=w,c=e,d=r);
DMux(in=q,sel=sel[0],a=a,b=b);
DMux(in=w,sel=sel[0],a=c,b=d);
line 22-> DMux(in=e,sel=sel[0],a=e,b=f);
DMux(in=r,sel=sel[0],a=g,b=h);
}
its showing an error message which says: in line 22 can't connect gate's output pin
to part
what does that mean??
can anyone help me..